Hydrogels represent a desirable class of materials for the manufacture of various biomedical devices, including contact lenses. A hydrogel is a hydrated cross-linked polymeric system that contains water in an equilibrium state. Hydrogel lenses offer relatively high oxygen permeability as well as desirable biocompatibility and comfort.
In a typical process for the manufacture of hydrogel polymeric contact lenses, a composition containing a diluent and suitable monomers is charged to a mold and cured. The molded lens can be subjected to machining operations such as lathe cutting, buffing, and polishing and further subjected to extraction, hydration, and sterilization procedures.
Generally, in the manufacture of contact lenses, some of the monomer mix components are not fully polymerized. The incompletely polymerized material from the polymerization process may affect optical clarity or be harmful to the eye. Residual material, which may be either hydrophilic or hydrophobic, include solvents, unreacted monomers, or low molecular weight oligomers. Hydrophilic residual materials can be extracted by water; hydrophobic residual components, referred to herein as “extractables,” are typically removed by extraction with water-miscible organic solvents, in particular, alcohols such as isopropanol. Following the alcohol extraction process, the lens needs to be hydrated by treatment with water before being sterilized by, for example, autoclaving in buffered saline. A typical extraction procedure is described in the Examples of U.S. Pat. No. 5,260,000 and Example B-11 of U.S. Pat. No. 5,789,461, in which contact lenses are removed from the molds in which they were formed and extracted with isopropanol. As an alternative extraction process, U.S. Pat. No. 5,607,518, and PCT Publications WO 95/20476 and WO 98/07554, disclose a method of contacting a contact lens with carbon dioxide, which may be mixed with isopropanol, to extract residual material from a contact lens.
A drawback of extracting with isopropanol for commercial scale manufacturing is that the replacement and disposal of relatively large volumes of spent solvent may be required, which is undesirable both economically and environmentally. The present invention provides for reducing the amount of spent extraction solvent in the manufacture of biomedical devices.